A wide variety of bowel diseases are related to the inflammatory processes. Two of the most important inflammatory conditions are ulcerative colitis (UC) and Crohn's disease (CD). UC is a chronic inflammatory condition of the internal lining of the colon. It extends from the rectum and can involve the entire colon. CD can involve the entire gastrointestinal (GI) tract but is usually limited to the small and large intestine. CD can extend through the bowel wall leading to other complications. About 20% of patients with CD have disease isolated to the colon. Both UC and CD are chronic conditions, and treatment typically follows a two-phase treatment approach: induction and then maintenance of remission. UC and CD are characterized by abdominal pain, bloody diarrhea, and bowel wall inflammation. For many patients, the disease is episodic, occurring as a cycle of flares and remissions with considerable morbidity. Symptoms can be mild or very severe and disabling. They can develop gradually or have a sudden onset.
Approximately one million Americans suffer with either UC or CD. In Western Europe and the United States the prevalence of UC is 70 to 150 per 100,000 while the prevalence of CD is 40 to 100 per 100,000. These diseases can affect persons of any age, but are more common in the second and third decades. Males and females are equally affected. Risk of disease is higher in some ethnic groups than others. Overall, the incidence of UC appears to be stabilizing, but the incidence of CD is increasing, especially among young people.
The causes of UC and CD are unknown, although genetic predisposition, infectious bacterial and viral agents, as well as environmental factors are suspected to play a role. Recent experimental and clinical studies suggest that the initiation and pathogenesis of CD and UC are multifactorial, involving interactions among genetic, environmental, and immune factors. Regardless of exactly how these interactions ultimately promote chronic gut inflammation, it is becoming increasingly apparent that the immune system plays a critical role in disease pathogenesis.
Current therapies for inflammatory bowel diseases fall into 4 classes: 1) corticosteroids 2) aminosalicylates, 3) immunomodulators and 4) antibiotics. Aminosalicylate drugs such as sulfasalazine or mesalamine are the mainstay of treatment for mild to moderate disease. Immunomodulatory agents such as azathioprine and 6-mercaptopurine are used as steroid-sparing agents but have a variety of adverse side effects, often precluding use in many patients. Additional immunomodulators such as monoclonal antibodies against tumor necrosis factor α (anti-TNFα) are effective in some patients with Crohn's disease.
Following introduction into clinical medicine for the treatment of rheumatoid arthritis 40 years ago, aminosalicylates (e.g., 5-ASA) have become the primary treatment for ulcerative colitis (UC). Aminosalicylates (e.g., 5-ASA) are first-line inductive agents for the treatment of mildly to moderately active disease, as well as the primary maintenance therapy for remitted UC, and are used in conjunction with corticosteroids during the transition from inductive to maintenance therapy.
Sulfasalazine was the original prototype aminosalicylate and was designed with the concept of combining an anti-bacterial agent (sulfapyridine) and an anti-inflammatory agent (5-ASA):

Although the mode of action of sulfasalazine is not clearly understood, multiple clinical studies indicate that the major therapeutic action resides in the 5-ASA moiety. The primary limitation of sulfasalazine is the significant rate of adverse events related to the sulfapyridine moiety, thereby compromising the clinical usefulness of sulfasalazine. As many as 30 to 40 percent of patients are unable to tolerate the doses required to provide optimal treatment benefits.
Commercially available products (mesalamine, ASACOL®, PENTASA®, ROWASA®) use various means of delivering 5-ASA to inflamed intestinal mucosa. All of these compounds deliver 5-ASA without the sulfapyridine component of sulfasalazine that causes most of the adverse reactions.
Olsalazine, having the following formula, has been used to treat ulcerative colitis.

In addition to being relatively expensive to make, olsalazine can have adverse side effects, including diarrhea.
It is known to use azathioprine (6-(1-methyl-4-nitroimidazol-5-ylthio)purine) in the treatment of inflammatory bowel disease. Azathioprine has the following chemical structure:

It is also known to use 6-mercaptopurine, a metabolite of azathioprine, to treat inflammatory bowel disease. 6-mercaptopurine has the following chemical structure:

Methotrexate (L-4-amino-N10-methylpteroyl-glutamic acid) has also been used to treat inflammatory bowel disease. Methotrexate has the following chemical structure:

Actarit (4-acetylaminophenylacetic acid) is an immunomodulatory drug that was approved in Japan in 1994 for use in the treatment of rheumatoid arthritis. Four-aininophenylacetic acid (4-APAA) is a precursor to actarit and in vivo studies demonstrate that 4-APAA undergoes acetylation to form actarit. Both actarit and 4-APAA possess immunomodulatory activity.
The polypeptide cyclosporine, which has traditionally been given to transplant patients to prevent organ rejection, has also been used to treat inflammatory bowel disease. The use of cyclosporine to treat IBD can be limited, however, by the various side effects associated with this medication. These side effects include high blood pressure, kidney damage, tremors, headaches, seizures, excessive hair growth, excessive gum growth, confusion, coma, and gout.